Finishing of artificial leather



sept. 24, 1935. q M. o. SCHUR ETA@ 2,015,440

FINISHING OF ARTIFICIAL LEATHER Filed April 11, 1932 @wi/WJ p Jw @ff/g4 @M v Patented Sept.l 24, v1,935 l FINISIIING o F ARTIFICIAL LEATHER Milton o. schul and Benjamin G. um, Berlin, Nr H., assignors to Brown Company, Berlin, N. H., a corporation of Maine Application April 11, 1932, Serial No. (504,644y

4 Claims.

This invention relates to the finishing of articial leather, more particularly of a kind designed for use in shoe uppers or in other connections where it is important or desired that sur- 5 face appearance and properties closely approach 15 papermaki'ng type can thus be combined with rub- 'ber or rubber compounds into artificial leathers simulating the natural article in many important respects. It has, however, been found exceedingly diiiicult to finish such leathers satisfactorily, that is, to provide a surface which simulates the grain or skin side of the naturalcommodity in such important aspects as appearance, mechanical properties, and ability to' take a leather dressing or finish properly. We have'found that We can provide the desired surface on artificial leather of the foregoing general types, if we preform a skin or pellicle from suitable compositions and combine or amalgamate the artificial leather with the preformed skin as a top sheathing. When it is desired to use a preformed skin too thin to be self-sustaining and to be handled properly, it may be deposited on a paper backing and kept thereon until it is transferred to the base of artificial leather, whereupon the paper may be removed. The skin is preferably preformed by spraying the skin-forming composition as on a gelatine-coated, so-called transfer paperr., A typical skin-forming composition, such as We use, contains both latex and glue as vessential components, the glue content of the skin being insolubilized or tanned either on the transfer paper or after the skin has been transferred to and combined with the artificial leather. The glue serves to toughen the skin, as

well as to render it comparatively short, by

which we mean that should a small part of the skin be scuied or lifted from the artificial leather base and then pulled, rather than causing the removal or peeling of the whole skin, it breaks after being stretched to only a comparatively in the case of the glue, the rubber content of the film may undergo vulcanizing while the skin is on the transfer paper or after transfer'has been accomplished. 'I'he skin-forming composition may contain a suitable dye or pigment designed to 5 impart the desired color to the artificial leather. We have found, however, that 'improved results. maybe secured by spraying so-called printing inks whose liquid vehicle is preferably of a nonaqueous, drying character, onto the transfer pal0 per, and then applying the skin-forming composition thereto. v On the accompanying legended drawing, we have'illustrated a fragment of the 'product embodying our invention.

Exemplary procedures falling within the pur- 15 view of our invention may be carried out in various ways, but we shall deal with specific procedures which we have practised with eminently satisfactory results. The artificial leather with which we worked wasvdesigned specifically for use 20 in shoe uppers and was prepared byimpregnat-v ing a waterlaid web of refined wood pulp with a prevulcanized latex composition containing-additional vulcanizing ingredients, an anti-oxidant, and glycerine, andthen dryingY the impregnated 25 web at elevated temperature. An artificial leather containing any other suitable fibrous foundation and prepared through impregnation with properly compounded latices or equivalent liquid rubber compositions might, however, well be em- 30 ployed. The particular artificial leather with which we were working is preferably scoured on its surface, as by frictional contact with rolls covered with paper, emery cloth, or other abrasive, which removes ysurface blemishes therefrom. 35

It may then be staked, or otherwise mechanically worked so as to acquire enhanced softness, pliability, and lleather-like feel, and then compacted in a press having nicely nished platens, which impart smoothness thereto. It is then cov- 40 ered with a preformed skin, which is prepared from a mixture of latex (either unvulcanized or vulcanized) and glue. Specifically, we may use for preforming the skin a composition whose total solids content is made up of 85% latex sol- 45 ids, 1.7% colloidal sulphurl 4.25% colloidal zinc oxide, 0.785% of suitablevulcanizing accelerator, 0.43% of suitable anti-oxidant, 6.3% glue or gelatine, and 1.5% of suitable water-soluble dye. Such a composition may be properly sprayedat a 50 solids content of about 30% onto a gelatine-coated, so-called transfer paper, to form a skin or pell licle thereon. In applying the composition to the paper, We may fasten a at sheet of the paper at its four corners, by means of rubber bands, to

` four pegs, so that although the sheet is restrained from curling, it can expand and contract freely and uniformly. The composition is allowed to dry on the paper backingto form the desired skin.'

a little latex is preferablyV sprayed onto the scoured surface of the artificial leather base, and 1 the skin carried by the paper backing is stuck onto the prepared surface of the base, under mild pressure. The backing is-` then moistened with water and peeled from the articial leather l ten minutes to an atmosphere at 220 F.

We have found'that the results may be further improved if the gelatine-coated transfer paper is first sprayed with a printing ink and the skinforming composition is applied thereto. We prefer to use a printing ink containing about 20% to 25% pigment and '15% to 80% boiled linseed oil, the mixture preferably being cut or diluted with toluol or other suitable volatile solvent, in the ratio of about 1 part of ink to about `3 parts of solvent, beforethe spraying operation, so as to facilitate spraying. Only about 1.0 to 1.5 grams of ink solids need be deposited per square foot of paper area. to yield an ink film of the desired character. Drying oils other than linseed may be used as the ink vehicle, and so, too, suitable quantities of gums, resins, and dyes may form part of the ink composition, as is sometimes thecase in printing inks. Since the ink is non-aqueous, it does not tend to curl or otherwise distort the gelatine-coated paper, even during the subsequent formation of the skin thereon, as the ink forms a waterproof barrier between the paper backing and subjection of'the comparatively thick artificial leather base to the action of glue-insolubilizing agents and heat. Thus, the transfer sheet may be subjected to the action of formaldehyde fumes at room temperature for about fifteen to eighteen hours, and a temperature of 220 F. for about ten minutes, for the purpose of transforming the skin to the desired condition.

In accomplishing a transfer of the preformedV skin to the base of artificial leather, we prefer to use an hydraulic press having a yielding bed and a' highly polished platen heated to a temperature of about 200 to 210 F., at which temperature a tenacious bonding of the skin to the artificial leather base is promoted. The artificial leather is placed in the press and the transfer i sheet is superposed thereon, with the preformed skin lying next to the artificial leather surface' and the plain paper face lying next to the hot platen. The platen is brought down on the superposed sheets to exert a pressure of 'about 40 to 50 pounds per square inch, and this pressure is maintained for about two or more minutes. 'I'he combined sheets are removed from the press, allowed to cool, and the paper ply is wetted with water and removed as ordinarily. 'I'he artificial leather has thus acquired a properly colored skin or a skin carying a film of ink. In either event, the usual water finish, clear or slightly dyed, may

be swabbed directly onto the surface, as is done 5 in the finishing of natural leather. T'he finish Y may, for example, be an aqueous mixture containing casein, blood albumin, and formaldehyde.

The results obtained by the practice of our invention are very gratifying, in that the finished lo article resembles natural leather, more particularly of the calf variety, very closely. The preformed skin or ink film, having been dried against a verysmooth surface, presents a remarkably uniform and homogeneous appearance, which perl5 sists even after the leather dressing or finish is applied. Heretofore, it was nigh impossible to produce artificial leather whose surface was free from visible pits or other surface blemishes, which were rendered all the more conspicuous by the 20 leather dressing or finish.

If desired, the skin-forming composition which we employ may contain powdered cellulose, e. g., chemical wood pulp or the like, mechanically reduced, as in a ball mill, to a particle size preferably less than about 200 mesh. The function of the pulverulent cellulose is to form pores in the skin, as well as to improve its feel and the adhesion of the leather finish thereto. It is not, however, an indispensable ingredient in the skinforming composition. If desired, the transfer paper may be embossed priorto the application of the ink and/ or skin-forming composition thereto, so as to impart the desired embossed effect to the surface of the artificial leather on which 3 5 the preformed skin and, if desired, ink film is imposed.

We have mentioned the fact that we preferably employ so-called vtransfer papers as the backing on which a skin of the proper composition is prev40 formed, along with an underlying film of so-called printing ink, if desired. Such a backing serves to sustain the preformed skin and, if desired, film of printing ink, until these preformed layers are transferred to the properly prepared base of arti- 4I ficial leather. As the transfer paper, we prefer to use, as already indicated,` the usual gelatinecoated transfer paper or its equivalent. The gelatine coating serves as an insulating layer between the paper backing and the skin, and, if desired, film of printing ink deposited on the layer for transfer purposes. 'Ihe coating of gelatine, capable of being softened by water, permits the removal of the paper backing after the desired transfer has, been effected, upon wetting of the paper, with- Il out disturbing or injuring the transferred skin and/or, ink film. Any other suitably coated transfer papers, e. g., papers coated with dextrine paste orsimilar water-soluble material, are serviceable as the backing or sustaining layer on which W the skin and, if desired, ink film are preformed. In using the expression transfer paper" in the appended claims, we mean a paper which is prepared for transfer purpose and accordingly contains an insulating layer of gelatine', dextrine 05 paste, or the like, functioning as an insulator and permitting subsequent removal of the paper backing from the article to which a transfer of the skin and, if desired, ink film deposited thereon has been made. In depositing the skin-forming 7 composition and so, too, the printing ink on the transfer paper, we may adopt any suitable mode of application, but, -as already stated, we prefer to efiect deposition by spraying. Thus, the spraymg of printing mk is conducive to a preformed film which when transferred tothe artificial leather base lends character. to the nished article. We have observed, for example, that when we finish artificial leathers in accordance with our invention, by using a sprayed, preformed film to produce a finished article simulating black calfskin, the finished surface, rather than having a dead black, painted appearance or a glazed appearance like patent leather or oil cloth, has a surprisingly natural or life-like appearance, and that the film has a fine grain akin to that occurring on the grain side of natural leather. This grain-like structure is perhaps caused by the air entrained in the sprayedA film, or by the imperfeet coverage effected by spraying. Although not completely substantiated by us, we believe that the ink when dried against the gelatine film adsorbs the latter so that when the transfer paper is peeled oiffrom the artificial leather, a minute film of gelatine remains on the ink, even though the ink surface may be washed in'running Water as is usually done after transfer papers are re-I moved in ordinary transfer work. The adsorbed gelatine, we believe, assists in lending to the ink film a characteristic grain-like appearance, highly valuable in the manufacture of artificial leather. Whether the foregoing belief is right or not, it is true that we have thus far obtained our best results by spraying the ink directly onto the transfer paper.

It is preferable to effect both the insolubillzation of the glue content and the vulcanization of the rubber content of the performed skin while it is still being sustained by the thin backing of transfer paper. It is, however, possible, as already indicated, to accomplish this after the skin has been transferred to the artificial leather base. It might further be mentioned that the glue content of the skin could be left therein in 1 ficial leather base to the desired color, a prea Water-soluble condition, and/or the rubber content of the skin left therein in unvulcanized condition, but the best characteristics are developed in the preformed skin only after the steps of in- 'solubilization and vulcanization have been performed. As tothe matter of nishing the artiformed film of ink or the addition of dyes or pigments to the skin-forming composition may be relied uponto furnish the desired coloring effect. The formation of a distinct film of printingink has already been emphasized as being by far the preferable expedient, although this may be cou- `pled with a simultaneous use of dyes or pigments in the skin-forming composition to afford maximum depth of coloration in the finishedl artificial leather. y

While we have indicated that we prefer to form the skin from a mixture of latex and glue, the glue may be omitted or replaced by other suitable compoundingingredients without departing from the scope of the present invention. Similarly, although we prefer to use a printing ink with an oil base, any other suitable type of dressing may be applied to the transfer paper before the skin coat is formed on it.

We claim:

l. A method which comprises spraying a nonaqueous printing ink on a transfer paper to form a film thereon, spraying a latex-and-glue mixture on said film to deposit a skin thereon, drying said lm and skin, insolubilizing the glue content and vulcanizing the rubber content of said skin, superposing said preformed skin and film junder heat and pressure while carried by said paper backing on a rubber-impregnated fibrous foundation to cause a bonding of said skin and film to said foundation, and removing said paper backing. v

2. An artificial leather comprising a layer of felted fibrous material impregnated with a vulcanized residuum of rubber latex and having a coating of glue and latex mixture united thereto and forming a smooth and homogeneous surface. 1

3. A method which comprises impregnating a felted brous web with latex, superposing under yfoundation having a coating of a latex and glue mixture united thereto and forming a smooth and homogeneous surface.

MILTON O. SCHUR.

BENJAMIN G. HOOS. 

